1. Field of the Invention
The present invention is in the field of telecommunications, and more specifically it relates to a method of optimizing the performance of a mobile terminal comprising a radio communication module, a central computing unit and a plurality of data processing software components. The present invention also relates to a mobile terminal.
2. Description of the Related Art
To prepare for possible handovers in a mobile telecommunication network, a mobile unit (UE; user equipment) in communication has to identify neighboring cells. For this, the mobile applies a procedure of searching for cells that comprises the step of performing measurements on neighboring cells, which allows for switching to the cell that offers an optimal communication quality. In searching for cells, a major problem arises when the sampling clock of the mobile is imprecise and/or when there is a Doppler deviation between the base station with which the mobile is in communication and the cell the mobile should identify.
A method for solving this problem is described in French patent application No. 02 07617 filed by the present applicant on Jun. 20, 2002. The solution proposed in the above application includes the step of applying digital filtering to the measurement samples collected in a plurality of time windows so as to give a predominant weight to the measurements performed in the most recent time windows. It should be noted that this solution does not take into account the traveling speed of the mobile terminal in the cellular network.
Moreover, detection performance of mobile terminals in a cellular network is highly dependent on the channel propagation properties. Degradation of the information carried by a transmitted signal in terms of amplitude, phase and/or frequency may be caused by these properties. This results in an increase in bit error rate (BER) and deterioration of global service quality offered.
To correct this degradation, a technique known in the prior art comprises the steps of estimating the impulse response (CIR: Channel Impulse Response) of the propagation channel and applying to the received signal a correction calculated according to the estimation. The precision of this estimation significantly varies according to the traveling speed of the terminal. To improve the precision, a known technique comprises the step of applying particular digital filtering, such as for example the filtering based on the technique called WMSA (Weighted Multi-slot Averaging) described in the document by H. Andoh, M. Sawahashi and F. Adachi, “Channel estimation filter using time-multiplexed pilot channel for coherent RAKE combining in DS-CDMA mobile radio,” IEICE Trans. Commun., Vol. E81-B, No. 7, July 1998.
A disadvantage of this method comes from the fact that to calculate the coefficients of the digital filter, it is necessary to know a priori the dynamic properties of the channel that are directly related to the traveling speed of the terminal.
Furthermore, studies made public specifically in the document by H. Holma and A. Toskala, “WCDMA for UMTS,” Wiley & Sons, 2000 shows that closed-loop power control is ineffective for speeds over 100 Km/h. It is also futile to send power control commands to the base station when this speed is surpassed.
A first solution to this problem would consist of completely stopping the transmission of these commands. However, this is not now allowed by current technical specifications.